Value Of Gap Parameter Research Articles

Optical properties of biased bilayer graphene due to gap parameter effects

We address the optical conductivity of undoped bilayer graphene in the presence of a finite bias voltage at finite temperature. The effects of gap parameter and stacking type on optical conductivity are discussed in the context of tight binding model Hamiltonian. Green’s function approach has been implemented to find the behavior of optical conductivity of bilayer graphene within linear response theory. We have found the frequency dependence of optical conductivity for different values of gap parameter and bias voltage. Also the dependence of optical conductivity on the temperature has been investigated in details. A peak appears in the plot of optical conductivity versus frequency for different values of temperatures and bias voltage. Furthermore we find the frequency position of broad peak in optical conductivity goes to higher values with increase of gap parameter for both bernal and simple stacked bilayer graphenes.

The Effects of Next-to-Nearest Neighbor Hopping Amplitude on Electrical Properties of Graphene Like Nanotube Structure

We have addressed density of states and electrical conductivity of doped graphene like nanotubes for both zigzag and armchair types in the context of tight binding model hamiltonian. The effects of next nearest neighbor hopping amplitude for electrons and gap parameter on electronic density of states and electrical conductivity have been investigated. Green’s function approach has been implemented to find the behavior of electrical conductivity of nanotube within linear response theory. We have found the temperature dependence of electrical conductivity for different values of gap parameter and tube diameter in the presence of neat nearest neighbor hopping integral. The results of electrical conductivity show the increase of diameter leads to increase the conductivity of both zigzag and armchair nanotubes. However the increase of chemical potential reduces the conductivity of armchair nanotube. In the presence of next-to-nearest neighbor hopping amplitude, the density of states results of nanotubes loses its symmetry with respect to energy.

Electrical conductivity of undoped bilayer Graphene: Beyond nearest neighbor approximation

We have addressed density of states and electrical conductivity of undoped biased bilayer graphene for both AA and AB stacking in the context of tight binding model hamiltonian. The effects of next nearest neighbor hopping amplitude for electrons and gap parameter on electronic density of states and electrical conductivity have been investigated. Green’s function approach has been implemented to find the behavior of electrical conductivity of bilayer graphene within linear response theory. We have found the temperature dependence of electrical conductivity for different values of gap parameter and bias voltage in the presence of neat nearest neighbor hopping integral. Our results for density of states of bilayer graphene in the presence of gap parameter show the increase of bias voltage reduces the band gap width. Also a peak in the dependence of thermal conductivity on temperature has been observed for all physical parameters. An anisotropic behavior for electrical conductivity of unbiased simple bilayer graphene in the presence of gap parameter has been resulted.

Effects of electron-phonon coupling and magnetic field on electrical conductivity of monolayer graphene

Abstract Electronic properties of gapped graphene structure taking into account the effects of interaction between electrons and Einstein phonons have been addressed. Specially we study the temperature dependence of electrical conductivity and density of states of the structure. The effects of gap parameter, magnetic field and electron doping on electrical conductivity of the system have been studied. Gap parameter is defined as the on-site energy difference of atoms on two different sublattices of honeycomb structure. Green’s function method has been implemented to obtain electronic density of states of the system in the context of Holstein model Hamiltonian. One loop electronic self-energy of the model Hamiltonian has been obtained in order to find interacting electronic Green’s function. The electrical conductivity of graphene structure in the presence of electron-phonon coupling can be readily found using interacting Green’s function based on Kubo formula. We present the numerical results of energy dependence of density of states for different values of gap parameter and magnetic field in the presence of Holstein phonons. Finally the temperature dependence of electrical conductivity of gapped graphene structure due to electron phonon interaction and magnetic has been investigated. Our results show turning on magnetic field leads to appear double van Hov singularity for each value of electron phonon coupling.

Dynamical quasiparticle properties of gapped monolayer graphene in the presence of Holstein phonons

We have calculated the quasiparticle particle self-energy and spectral function in a graphene plane when a symmetry breaking of the sublattice is occurred. Holstein model Hamiltonian has been applied to describe the electron dynamics in the presence of lattice vibrations. This model Hamiltonian takes into account the effects of interaction between electrons and Einstein phonons beyond the usual Dirac-cone approximation. Specially, the effects of gap parameter and electron-phonon coupling strength on spectral function, inelastic scattering lifetime and band gap renormalization have been studied. Also the electron density dependence of inelastic scattering lifetime for different values of gap parameter has been investigated. In order to find the quasiparticle excitation spectrum of the interacting electronic system, we have studied the frequency dependence of spectral function for different physical parameters. Our results show the intensity of broad peak in frequency dependence of spectral function reduces with electron-phonon coupling strength. However the intensity of quasiparticle particle peak increases with coupling strength. The increase of gap parameter leads to appear sharp quasiparticle peak with high intensity in spectral function. The frequency dependence of sharp peak goes to higher frequency with gap parameter. Also the gap parameter dependence of inverse of scattering life time shows a sudden change for all values of coupling constant. Finally band gap renormalization enhances with electron-phonon coupling constant at fixed electron density.

The study of dynamical quasiparticle properties of undoped graphene nanoribbon

We have calculated the quasiparticle particle self-energy and spectral function in an undoped graphene nanoribbon when a symmetry breaking of the sublattice is occurred. Hubbard model Hamiltonian has been applied to describe the electron dynamics in the structure. Using the many body G0W approach and Green's function technique, we have found the dynamical quasiparticle properties of electrons on nanoribbon structure. Also random phase approximation has been exploited to calculate electronic self-energy of the system. The difference between on-site energies of atoms on two sublattices is named gap parameter. Specially, the effects of gap parameter and Hubbard parameter on spectral function, inelastic scattering lifetime and band gap renormalization have been studied. Also the wave vector dependence of inelastic scattering lifetime for different values of gap parameter has been investigated. In order to find the quasiparticle excitation spectrum of the interacting electronic system, we have studied the frequency dependence of spectral function for different physical parameters.

Effect of Gap Parameter on Electronic Heat Capacity and Magnetic Susceptibility of Graphene in the Presence of Holstein Phonons

Thermodynamic properties of gapped graphene-like structures by considering the effects of interaction between electrons and Holstein phonons have been studied. Particularly, we study the heat capacity and paramagnetic susceptibility of structures as a function of temperature within the Green’s function method with the help of Holstein model. The paramagnetic susceptibility and heat capacity can be derived by using density of states based on the Kubo formula. We have found the energy dependence of density of states for various values of gap in the presence of Holstein phonons. Finally, the temperature behaviors of specific heat and spin susceptibility of gapped graphene structure due to electron-phonon coupling have been investigated. Our results show the electron-phonon interaction leads to the appearance of a double van Hov singularity for each value of gap parameter. Also, electron-phonon coupling affects the value of heat capacity and magnetic susceptibility at low temperatures.

Optical properties of gapped graphene structure in the presence of electron-phonon interaction: A full band approach

We compute the optical conductivity of gapped graphene taking into account the effects of interaction between electrons and Einstein phonons beyond the usual Dirac-cone approximation. Our study is based on the Kubo formula that is established upon the retarded self-energy. Specially we report the frequency dependence of optical absorption of the structure. We find numerical results for frequency dependence of optical absorption for different values of gap parameter in the presence of Holstein phonons. We have also studied the effects of electron-phonon coupling strength and electronic concentration on the behavior of optical absorption of the gapped graphene structure. Our results show the increase of electronic chemical potential in doped case leads to appear optical band gap in the structure. This optical gap arises from Pauli blocking of vertical transitions when conduction band is doped. Electron-phonon coupling broadens the peak in the optical spectral and decreases the intensity of optical absorption. However the frequency position of the peak is not considerably affected by electron-phonon coupling.

Effect of superconducting correlation on the localization of quasiparticles in low dimensions.

Localization lengths of superconducting quasiparticles $\lambda_s$ are evaluated and compared with the corresponding normal state values $\lambda_n$ in one and two dimensional lattices. The effect of superconducting correlation on the localization of quasiparticles is generally stronger in an off-site pairing state than in an on-site pairing state. The modification of superconducting correlation to $\lambda$ is strongly correlated with the density of states (DOS) of superconducting quasiparticles. $\lambda_s$ drops within the energy gap but is largely enhanced around energies where DOS peaks appear. For a gapless pairing state in 1D or a d-wave pairing state in 2D, $\lambda_s/ \lambda_n$ at the Fermi energy $E_F$ is of order 1 and determined purely by the value of gap parameter not by the random potential. For the d-wave pairing state, the localization effect is largely weakened compared with the corresponding normal state and quasiparticles with energies close to $E_F$ are more strongly localized than other low energy quasiparticles.